In the prior art quadrant detectors, the use of area detectors, suffered from the fact that large area photoelectric detectors have very poor sensitivities, high capacitance, slow response and poor signal to noise ratios. Also, area detectors are available for only a limited range of wave lengths. In prior art quadrant detectors, the angular field of view is limited by the size of the detector. Thus, to obtain a large angular field of view, the use of costly large area detectors is required.
Presently in the state of the art, there are available high quality point detectors, which do not have the limitations of area detectors. Due to their small area, however, no quadrant detector system is presently available to make use of these point detectors.